The construction of buildings formed of poured-in-place concrete and with exterior walls of concrete panels, has been in use for many years. Conventional techniques involve the use of, in general, first of all pouring concrete columns, internally reinforced with rebars, then erecting horizontal form work for pouring a floor slab, and then pouring an entire floor of concrete in situ on the form work at the building site. Usually the construction proceeds by pouring further columns and then pouring floors in situ, to reach the appropriate height of the building. Exterior walls are often erected of precast concrete panels.
Such systems are labour intensive, and slow and expensive. The systems are also wasteful of materials such as form work, and wasteful of concrete and rebars. The form work is usually custom made on site and erected on a large number of internal portable posts. The form work must be laid out and supported accurately so that the pouring of the floor can proceed. The resulting floors are poured in one piece in the majority of cases. Rebars are incorporated throughout such a floor, and the floor is connected to the upper ends of the vertical frame s, usually by connecting rebars. The volumes of concrete used in such a system are very considerable. The thickness and weight of the rebars is also considerable. The total weight per floor of the building is therefore made up of relatively massive monolithic slabs of concrete, and large volumes and lengths of heavy rebars. This is wasteful in terms of costs and materials. It also restricts the height of the building since the footings must be designed to carry a certain weight of construction materials when the building is erected and also the occupants of the building and all their equipment.
In addition to all this, the onsite labour costs are considerable. Typically, onsite labour rates will be two or three times the hourly rate paid to employees in the factory. Clearly it is desirable to both reduce the volume of concrete material required and to reduce the weight of the rebars. It is further desirable to reduce the amount of form work which must be erected to support the floors while they are being poured, and cured. It is also desirable to reduce, as far as possible, the onsite labour costs.
It is therefore desirable to manufacture as far as possible, precast concrete floor components in a factory remote from the building site, and transport such precast floor components to the site and erect them in position. This will greatly reduce the onsite labour costs. It will reduce the time taken to pour concrete on site.
An additional factor is that by manufacturing modular precast components, stress factors can be incorporated in the modular components, which permit considerable reduction in the amount of concrete and rebars required, without any loss of strength to the building.
Clearly by reducing the weight of the volume and the rebars in the building, it is possible to either reduce the building footings or alternatively to build higher, using the same footings.
One modular system is disclosed in Russian patent No. 2376424; Inventor: Nikolay P. Tikhovskiy; Priority Date: Jun. 3, 2008.
The system disclosed in this patent involves a floor made with the use of pre-cast flat solid concrete slabs, with rebar components extending out from the slabs. The slabs are then supported at floor level, leaving channel spaces between them. In this system the on site pouring time and volume of on site concrete required, and the form-work required is greatly reduced, compared with pouring an entire floor.
However, the floor slabs with rebars were still relatively massive.
It is has now been discovered that the plain flat slabs can be replaced with modular precast concrete caissons. The caissons are formed with massive, deep side walls, and a central slab portion of reduced thickness, supported by the side walls. These caissons may be formed in various shapes, typically square or rectangular but may be hexagonal, or even circular or other shapes, to suit the design of the building. The pre cast caissons are then supported in place at the building site, with their side walls spaced apart being supported by removable posts such as are well known in the art. Between the caisson side walls, channel spaces are defined, which are closed off by form work. Rebars are laid in the channel spaces between the caissons. Concrete beams are then poured on site in the channel spaces between the caissons. The concrete bonds with the side walls of the caissons thereby forming concrete beams, interconnecting and supporting the caissons. The caissons and the beams thus form a homogenous floor.
It is particularly advantageous to provide such caissons which have features capable of interlocking directly with the poured concrete of the beams without the need for interlocking rebars.
By this system, the caissons can be manufactured and precast away from the building site at a remote location, in a factory. The caissons can thus be poured under controlled conditions and can be cured under controlled conditions thereby ensuring the maximum performance of the concrete.
As explained above, the caissons are formed with planar floor slab portions, and downwardly dependent side walls surrounding the floor slab portions. The caisson side walls and the floor slab portion define a downwardly open hollow space.
The caisson side walls are deeper than the thickness of the caisson floor slab portions. As a result, when the form work closes off the channel spaces defined between the caisson side walls, the beams, which are formed by pouring concrete in situ in the channels, have a greater depth, than the beams in the aforesaid application. Depending upon the design of the building, it may still be necessary in some areas of the floor, to use the plain flat precast floor slabs of the aforesaid earlier application. In those cases the floor of the building will consist of a large number of modular precast concrete caissons, interconnected with poured-in-place concrete beams, and some other areas of precast floor slabs, interconnected with poured-in-place beams
The construction of the exterior walls of the building may use a variety of precast concrete slabs or many other different exterior building finishes. The building interior partition walls are made of precast concrete. Such interior partition walls are constructed of precast concrete wall panels. Such precast concrete wall panels will be erected side by side, with spaces between their edges so that they do not abut directly edge to edge. Such wall panels incorporate rebars which extend outwardly along the edges of the panels. Vertical form work is then erected along the spaces between the edges of adjacent wall panels, and vertical frame rebars are placed in position, and concrete is then poured in place, to form vertically extending frames holding the wall panels in position, and providing support for the building.